Molding cycle control method of an injection molder

ABSTRACT

A molding cycle control method of an injection molder includes a flow passage opening and closing mechanism which prevents a flow of a plasticized synthetic resin to be injected, aiming at shortening the time required for each molding cycle and the stability of weight value of molded products. The above-mentioned control method includes the flow passage opening and closing mechanism being closed under the state that the plasticized synthetic resin is injected and filled into a cavity of a mold and is applied with dwelling pressure. Thus, a dwelling process is conducted by the residual dwelling pressure at the mold side and simultaneously a measuring process for a next molding cycle is carried out at the screw side, thereby enabling the time required for each molding cycle to be shortened. Further, with the provision of the flow passage opening and closing mechanism and the check valve at the screw, a definite the predetermined value of resin pressure of the plasticized synthetic resin placed in the cylinder immediately before the injection and during the dwelling can be obtained. Furthermore, since a weight value of a molded product can be obtained through an operation, the injection molder can be controlled to keep constant the weight value of molded products constant.

FIELD OF THE INVENTION

The invention relates to a molding cycle control method of an injectionmolder comprising a flow passage opening and closing mechanism which isprovided between the inside for a cylinder in the injection molder and acavity of a mold to prevent a flow for plasticized synthetic resin,between the inside of the cylinder and the cavity, wherein a timerequired for each molding cycle is shortened and the weight of moldedproducts can be kept constant.

BACKGROUND OF THE INVENTION

Injection molding of plasticized synthetic resin, conducted by the useof an injection molder has a problem in that it is difficult to keep thequality of molded products constant by making up the shrinkage of theplasticized synthetic resin in cooling and setting in the cavity of themold. To solve the problem, various control methods for the injectionprocess have been proposed.

The art disclosed in Japanese Examined Patent Publication No. Hei.1-33331 (1989) is an example of an attempted solution to theabove-mentioned problem, wherein a screw or a plunger moved forward at ahigh speed in the material filling process is slowed during the dwellingprocess to apply dwelling pressure to the plasticized synthetic resinplaced inside the cavity, then, the screw or the plunger is locked inmovement and held in place until the plasticized synthetic resin insidethe gate of the mold is cooled and solidified(gate-sealed) to preventfurther of the plasticized synthetic resin between the inside ofcylinder and the cavity.

However, the gate-sealing is a function occurring inside the mold, sothat it is quite difficult to detect precisely when gate sealing occurs.Furthermore, the time when the gate-sealing occurs varies depending onsubtle changes of temperatures of the mold and the plasticized syntheticresin, so that the time the screw or the plunger is locked must be setexcessively long to ensure and completion of the gate sealing. Also,locking of the screw or the plunger needs a feed-back control device,resulting in requiring an expensive injection molder. Hence, it furtherleads to a problem of a low productivity due to a longer locking timeand a high cost of production due to the use of a complicated controldevice.

Also, to compensate for the shrinkage of the plasticized synthetic resincooled and set in the cavity, the conventional control method asabove-mentioned supplies a corresponding volumetric amount of materialto the shrinkage from the molded product itself by locking the screw orthe plunger until the gate is sealed in the dwelling process to preventa flow of the plasticized synthetic resin in the gate so as to releasethe pressure of the resin which has been compressed by the fillingoperation. By this method, the shrinkage can be made up and a moldedproduct of a fixed volume corresponding to an internal volume of thecavity can be provided. But, as long as the plasticized synthetic resinhas a compressibility, its density changes depending on the pressure andtemperatures, so that it is hard to keep a constant weight of a moldedproducts.

The present invention has been designed to overcome the above-mentionedproblems. An object of the invention is to provide a molding cyclecontrol method of an injection molder which method can shorten the timerequired for each molding cycle without using a complicated device yetkeep the weight of the molded products constant.

DISCLOSURE OF THE INVENTION

The molding cycle control method for an injection molder according tothe present invention is an injection molding cycle control method foran injection molder comprising a flow passage opening and closingmechanism which is provided between the inside of a cylinder in theinjection molder and a cavity of a mold which can block a flow of aplasticized synthetic resin between the inside of the cylinder and thecavity, the molding cycle control method, basically, being characterizedas comprising the following steps to achieve the above-mentioned object:

(a) a pre-injection pressing process wherein while the flow passageopening and closing mechanism is closed and the plasticized syntheticresin is prevented from flowing after the synthetic resin has beenplasticized and measured, a predetermined pushing force is applied to ascrew to set the resin pressure in the cylinder to a predeterminedvalue,

(b) a filling and dwelling process comprising a filling process whereinwhile the flow passage opening and closing mechanism is open to allowthe plasticized synthetic resin to flow, the screw is moved forward toinject and fill plasticized synthetic resin into a cavity of a mold, anda dwelling process wherein a predetermined pushing force is applied tothe screw in continuation to the filling process, the filling anddwelling process being conducted to fill a predetermined amount ofplasticized synthetic resin into the cavity,

(c) a measuring process wherein while the flow passage opening andclosing mechanism is closed to prevent a flow of plasticized syntheticresin, the screw is rotated and moved backward to measure apredetermined amount of plasticized synthetic resin for a next moldingcycle, and

(d) a suck-back process wherein while the flow passage opening andclosing mechanism is open to allow a flow of plasticized syntheticresin, the screw is moved backward, so that the pressure of plasticizedsynthetic resin placed between a gate of the mold and a front end of thescrew at its forward movement side is reduced.

It is preferable that a check valve be provided at the screw whichcloses during the pre-injection pressing process to prevent a flow ofthe plasticized synthetic resin between the flow passage opening andclosing mechanism and the check valve in the direction of the backwardmovement of the screw.

Also, in the filling and dwelling process, the predetermined amount ofthe plasticized synthetic resin to be filled in the cavity may bedetected from the screw's specific positional values or the plasticizedsynthetic resin pressure values placed in the cylinder or in the cavity,or also from a predetermined travel distance of the screw correspondingto its value, respectively, from a point where the screw is positionedimmediately before the injection operation. Furthermore, thepredetermined amount of the plasticized synthetic resin may berepresented by the following formula with a weight value G as follows.

    G=(1/V.sub.I -1/V.sub.H)×V+A×X/V.sub.H         ( 1)

wherein:

V_(I) : is a specific volume value of the plasticized synthetic resin onthe forward movement side of the front end of the screw in the cylinderimmediately before the injection operation;

V_(H) : is a specific volume value of the plasticized synthetic resinplaced on the forward movement side of the front end of the screw in thecylinder during the dwelling operation;

V: is a volume value of the plasticized synthetic resin on the forwardmovement side of the front end of the screw in the cylinder immediatelybefore the injection process;

A: is the internal sectional area of the cylinder;

X: is the travel distance of the screw from its position immediatelybefore the injection to its position during the dwelling operation.

It is preferable that during the above-mentioned dwelling process theflow passage opening and closing mechanism is closed while apredetermined pushing force is being applied to the screw.

Also, it is preferable that the suck-back process is conducted while theplasticized synthetic resin placed in the gate of the mold is solidifiedand the flow of the plasticized synthetic resin in the gate is blocked.The suck-back process may be carried out at any staged during themeasuring process or after the completion thereof.

Hence, according to the molding cycle control method of the injectionmolder of the present invention, the plasticized synthetic resin in themold and the plasticized synthetic resin in the screw do not affect eachother when the flow passage opening and closing mechanism is closed, sothat the separate processes may be conducted simultaneously. Forexample, when the flow passage opening and closing mechanism is closedduring the dwelling process while a predetermined pushing force isapplied to the screw for generating dwelling pressure for compensatingfor the shrinkage of the cooled plasticized synthetic resin, a residualdwelling pressure is created on the mold side of the mechanism wheredwelling is then continued while simultaneously, measuring for a nextmolding cycle can be immediately conducted on the screw side of themechanism, thereby shortening the time for each molding cycle.

Further, in the pre-injection pressing process, the flow passage openingand closing mechanism as well as the check valve provided at the screware closed and, the plasticized synthetic resin in the cylinder does notflow back, so that the pressure value of the plasticized synthetic resincan have a definite predetermined value immediately before the injectionoperation. Also, the resin pressure value of the resin during dwellingprocess can be set to a definite predetermined value. Hence, thepositional value of the screw, the plasticized synthetic resin pressuresin the cylinder or in the cavity, or the screw's predetermined traveldistance from its position where the screw is positioned immediatelybefore the injection may be detected to obtain a predetermined amount ofthe plasticized synthetic resin to be injected and filled in the cavity.Also, by applying the aforesaid formula (1), weight value of theplasticized synthetic resin to be injected and filled in the cavity canbe obtained to control the injection molder to provide molded productsof a constant weight.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 through 4 are explanatory drawings showing preferable examplesof the molding cycle control method of the injection molder according tothe present invention.

FIG. 1 is a longitudinal sectional schematic diagram of the entirety ofthe injection molder.

FIG. 2 is an enlarged, partial longitudinal sectional view of theinjection molder shown in FIG. 1.

FIG. 3 is a time chart of a molding cycle; and

FIG. 4 is longitudinal sectional views schematically showing operationalstates of the screw when the weight value of injected and filledplasticized synthetic resin is obtained.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Next, a concrete embodiment of the molding cycle control method of theinjection molder according to the present invention will be explainedwith reference to the accompanied drawings.

FIG. 1 shows a profile o the injection molder, wherein an injectionmolder 11 is connected to a mold 10 for preparing a molded productthrough a nozzle part 12. In a cylinder 13 of the injection molder 11 ismounted a screw 18 which melts and kneads resin pellets of theplastifiable synthetic resin material fed from a material hopper 14, andmeasures the melted and plasticized resin to inject and fill it into acavity 17 of the mold 10 through a flow passage 15 bored in the nozzlepart 12 and a gate 16 of the mold 10. Rotation of the screw 18 formelting and kneading the material resin pellets is controlled byoperating an electromagnetic flow valve 19, an electromagnetic pressurevalve 20 and a switch valve 21 through a controller 22 to supply anddischarge pressure oil from a pressure oil source 23 to a screw rotatingmotor 24 through a piping 25a. The screw 18 and the screw rotating motor24 are mounted on a base 26 which is driven to the right and left sidein the drawing by means of the pressure oil which is supplied anddischarged to a hydraulic piston device 27 from the pressure oil source23 through pipings 25b and 25c by controlling the electromagnetic flowvalve 19, electromagnetic pressure valve 20 and switch valve 21 with thecontroller 22. In other words, forward and backward movement of thescrew 18 with respect to the nozzle part 12 for measuring of theplasticized synthetic resin to be injected and injecting and filling ofthe measured plasticized synthetic resin into the cavity 17 of the mold10, and the application of a predetermined pushing force to the screw 18for providing a predetermined pressure of the plasticized syntheticresin in the cylinder 13 are carried out through the base 26 bysupplying and exhausting pressure oil to the hydraulic piston device 27.A screw position detector 28 which detects positional values of thescrew 18 is disposed on the base 26. The detected positional values aretransmitted to the controller 22 and an arithmetical unit 29 fordetermining the weight value of filled plasticized synthetic resin andthe like. To the arithmetical unit 29 are also transmitted thetemperature values from a resin temperature detector 30 which detectsthe temperature of the plasticized synthetic resin placed in thecylinder 13, the resin pressure values from a resin pressure detector 31which detects the resin pressure of the plasticized synthetic resinplaced in the cylinder 13 and the cavity resin pressure values from acavity pressure detector 32 which detects the resin pressure of theplasticized synthetic resin placed in the cavity 17 of the mold 10

In the flow passage 15 of the nozzle part 12 is provided a closing valve33 which constitutes the flow passage 15 opening and closing mechanismof the present invention and blocks the flow of the melted plasticizedsynthetic resin. Opening and closing of the closing valve 33 isaccomplished through the lever 35 by controlling an electromagneticdrive device 34.

As shown in FIG. 2, a ring-like shaped slidable valve member 39 which isaxially movable forward and backward is inserted between a conical frontend 36 of the screw 18 and a flange projection 38 at the end of spiral37. The ring-like shaped slidable valve member 39 is pressed andcontacted to the flange projection 38 when the pressure of theplasticized synthetic resin at the leftside of the drawing, in turn, atthe front end side of the screw 18 becomes higher, so that it preventsthe plasticized synthetic resin from flowing back to the right side inthe drawing. Thus, a check valve 40 consists of the flange projection 38and ring-like shaped slidable valve member 39.

Next, an embodiment of a molding cycle control method of an injectionmolder according to the present invention using the above-mentionedinjection molder will be explained referring to FIGS. 3 and 4.

(1) Pre-injection Pressing Process

After the synthetic resin is plasticized and measured, and while theclosing valve 33 is closed and the flow of the plasticized syntheticresin is blocked, a predetermined pushing force is applied to the screw18. Hence, the check valve 40 is closed by the pushing force applied tothe screw 18, so that the plasticized synthetic resin is blocked fromflowing in the direction of moving back of the screw 18, thereby theallowing the pressure of the synthetic resin in the cylinder 13 to be ata definite predetermined resin pressure value P_(I) which is detected bythe resin pressure detector 31 and transmitted to the arithmetical unit29. Also, a screw positional value S_(I) at the time detecting P_(I) isdetected by the screw position detector 28 and transmitted to thecontroller 22 and the arithmetical unit 29, and the temperature valuesT_(I) of the plasticized synthetic resin detected by the resintemperature detector 30 and is the transmitted to the arithmetical unit29. Specific values of the resin pressure value P_(I), screw positionalvalue S_(I) and temperature value T_(I) are supplied, as detected valuesobtained immediately before the injection operation, to the arithmeticalunit 29 for its determination of a weight value G (described later) ofthe plasticized synthetic resin to be filled in the cavity 17. (See FIG.4)

(2) Filling and Dwelling Process

While the closing valve 33 is open and the plasticized synthetic resincan flow, the screw 18 is moved forward to fill the plasticizedsynthetic resin into the cavity 17 of the mold 10 followed by applying apredetermined pushing force to the screw 18 to give a dwelling pressureto the plasticized synthetic resin filled in the cavity 17. While apredetermined pushing force is applied to the screw 18, the closingvalve 33 is closed to allow resin pressure the cylinder 13 to be at adefinite predetermined resin pressure value P_(H) which is detected bythe resin pressure detector 31 and transmitted to the arithmetical unit29. Also, while the closing valve 33 is closed, the screw positionalvalue S_(H) detected by the screw position detector 28 is transmitted tothe controller 22 and the arithmetical unit 29, and the temperaturevalue T_(H) of the plasticized synthetic resin detected by the resintemperature detector 30 is transmitted to the arithmetical unit 29.Specific values of the resin pressure value P_(H), screw positionalvalue S_(H) and temperature value T_(H) are supplied, as detected valuesobtained in the dwelling operation, to the arithmetical unit 29 in orderto be applied in the determination of a weight value G (described later)of the plasticized synthetic resin to be filled in the cavity 17. (SeeFIG. 4)

(3) The First Half of the Measuring Process

While the closing valve 33 is closed, as continued from the previousprocess, to block the plasticized synthetic resin from flowing, thescrew 18 is rotated and moved back to measure a predetermined ratio ofthe plasticized synthetic resin of a predetermined amount of the samefor a next molding cycle. In the previous process (2) of the filling anddwelling process, the closing valve 33, was closed while a predeterminedpushing force was being applied to the screw 18, so that the plasticizedsynthetic resin remaining in the cavity 17 has residual dwellingpressure even after the closing valve 33 is closed, which is the same asthat applied by the screw 18 due to the predetermined pushing force togive dwelling pressure to the plasticized synthetic resin. Hence, thepresent first half of the measuring process carries out the dwellingoperation through residual dwelling pressure, on the mold 10 side of thevalve 33 simultaneously with the measuring operation on the screw 18side of the valve 33.

(4) Suck-back Process

Which the plasticized synthetic resin in the gate 16 of the mold 10 isset (gate-sealed), the closing valve 33 is opened and due to the screw18 moving back, the pressure of plasticized synthetic resin between thegate 16 of mold 10 and the front end of the screw 18 at its forwardmovement side is lowered, so that leakage of the plasticized syntheticresin placed between the nozzle part 12 and the mold 10 or from theparting line thereof is prevented.

(5) The Latter Half of the Measuring Process

While the closing valve 33 is closed to block the plasticized syntheticresin from flowing, the screw 18 is rotated and moved back to measure aremaining portion of the plasticized synthetic resin in addition to thatmeasured in the previous (3) measuring process to reach thepredetermined amount of plasticized synthetic resin for a next moldingcycle.

In a series of molding processes above, the closing valve 33 is closedwhile a predetermined pushing force is applied to the screw 18 in thedwelling process, so that movement of the screw 18 does not affect themold 10 side. Hence, the mold 10 side has a residual dwelling pressurewith the dwelling operation being continued, and the screw 18 side isable to carry out measuring for a next molding cycle immediately afterthe closing of the closing valve 33. Thus, the dwelling process and themeasuring process run simultaneously, thereby shortening the timerequired for each molding cycle.

Both the closing valve 33 and the check valve 40 are closed immediatelybefore the injection (immediately after pre-injection pressing) andduring dwelling operation. Resin pressure of the plasticized syntheticresin placed between the closing valve 33 and the check valve 40 withthe screw 18 being so positioned in these circumstances indicatesdefinite predetermined values. Thus, in the arithmetical unit 29,specific volume value of the plasticized synthetic resin is obtainedfrom a known resin properties relation formula, such as PVT relationformula (resin pressure value--resin specific volume value--resintemperature values) by the use of the above values of the screwpositional values S_(I), S_(H), resin pressure values P_(I), P_(H) andresin temperature values T_(I), T_(H), and further, the weight value Gof plasticized synthetic resin to be filled in the cavity 17 is obtainedthrough an operation based on the following formula (1).

    G=(1/V.sub.I -1V.sub.H)×V+A×X/V.sub.H          (1)

wherein:

V₁ : is a specific volume value of plasticized synthetic resin on theforward movement side of the front end of the screw 18 in the cylinder13 immediately before the injection operation;

V_(H) : is a specific volume value of the plasticized synthetic resin onthe forward movement side of the front end of the screw 18 in thecylinder 13 during the dwelling operation;

V: is a volume value of the plasticized synthetic resin placed on theforward movement side of the front end of the screw 18 in the cylinder13 immediately before the injection (i.e., the internal volume value ofthe cylinder);

A: is the internal sectional area of the cylinder;

X: is the travel distance of the screw 18 from its position immediatelybefore the injection to its position during the dwelling operation(i.e., S_(I) -S_(H)).

The internal sectional area A of the cylinder in the formula (1) isobtained from the design value of the injection molder 11, and thevolume value V of the plasticized synthetic resin placed the front endof the screw 18 on the forward movement side in the cylinder 13immediately before the injection can be obtained from the cylinderinternal sectional area A and the screw positional value S_(I) throughthe operation by the arithmetical unit 29.

Even when a molding condition changes from a standard condition due toexternal disturbances and the like, molded products of a stable qualitycan be provided by controlling the injection molder on the basis of atraveling distance X of the screw 18 which value is obtained through theoperation of using the PVT relation formula (1) to form a molded productwith a target weight value G.

In the present embodiment, the weight value G of plasticized syntheticresin to be filled in the cavity 17 of the mold 10 is obtained throughthe operation. And, furthermore, the injection molder may be controlledby detecting the screw positional values, the resin pressure value ofplasticized synthetic resin placed in the cylinder 13 or in the cavity17, corresponding to the weight value G, respectively. When there is astable molding condition substantially without a change of the moldingcondition, or there is almost no change in the resin pressure valuesP_(I), P_(H), and the resin temperature value T_(I), T_(H), it isenough, for directly obtaining the weight value G, to detect that thescrew 18 is moved for a predetermined distance from a point where it ispositioned immediately before the injection.

The nearer the screw 18 is positioned to the nozzle part 12 in thesuck-back process, the more effectively the pressure of the plasticizedsynthetic resin can be lowered. In the present embodiment, the measuringprocess is divided into two with respect to the time when the gate 16 issealed, so that the first half of the measuring process includes thesuck-back process. Alternatively, the suck-back process may be conductedafter the completion of the measuring process depending on the kinds ofthe plasticized synthetic resin to be used, resin pressure values,shapes of the mold 10, volumes of the cavity 17 and the like.

INDUSTRIAL AVAILABILITY

According to the present invention, the dwelling process and themeasuring of the plasticized synthetic resin for a next molding cycleare carried out simultaneously, so that the time required for eachmolding cycle can be shortened. Also, even when the molding conditionchanges due to the external disturbances or the like, the weight valuesof molded products can be kept constant, thereby contributing to theimprovement of the productivity and the quality of products.

What is claimed is:
 1. A molding cycle control method for an injectionmolder comprising a cylinder with a screw therein and a flow passageopening and closing mechanism which is provided between the cylinder ofthe injection molder and a gate of a mold, the mold having a moldcavity, the opening and closing mechanism provided for the flow of aplasticized synthetic resin between the inside of the cylinder and thecavity of the mold, the method comprising the following steps:(a) apre-injection pressing process wherein after the synthetic resin isplasticized and measured, with the flow passage opening and closingmechanism closed to prevent the flow of the plasticized synthetic resin,a predetermined pushing force is applied to the screw to set the resinpressure value inside the cylinder equal to a predetermined value, (b) afilling and dwelling process comprising a filling process wherein withthe flow passage opening and closing mechanism open to allow theplasticized synthetic resin to flow, the screw is moved forward toinject and fill the plasticized synthetic resin into the cavity of themold, and a dwelling process to apply a predetermined pushing force tothe screw following the filling process, during which the flow passageopening and closing mechanism is closed the filling and dwelling processbeing conducted to fill a predetermined amount of the plasticizedsynthetic resin into the cavity, (c) a measuring process wherein withthe flow passage opening and closing mechanism closed to block the flowof plasticized synthetic resin, the screw is rotated and moved backwardto measure a predetermined amount of the plasticized synthetic resin fora next molding cycle, and (d) a suck-back process wherein with the flowpassage opening and closing mechanism open to allow the plasticizedsynthetic resin to flow, the screw is moved backward to lower thepressure of the plasticized synthetic resin located between the gate ofthe mold and the front end of the screw at its forward movement side. 2.The molding cycle control method of an injection molder as set forth inclaim 1, wherein in the pre-injection pressing process, a check valvemounted to the screw is closed to prevent a flow of the plasticizedsynthetic resin placed between the flow passage opening and closingmechanism and the check valve toward the direction of backward movementof the screw.
 3. The molding cycle control method of an injection molderas set forth in claims 1 or 2, wherein during the dwelling and fillingprocess, a predetermined amount of the plasticized synthetic resin to befilled in the cavity is determined based on the positional value of thescrew or pressure values of the plasticized synthetic resin placed inthe cylinder or in the cavity.
 4. The molding cycle control method of aninjection molder as set forth in claims 1 or 2, wherein during thedwelling and filling process, a predetermined amount of the plasticizedsynthetic resin to be filled in the cavity is determined on the basis ofa predetermined travel distance of the screw from the position where thescrew is positioned immediately before the injection.
 5. The moldingcycle control method of an injection molder as set forth in claims 1 or2, wherein a predetermined amount of the plasticized synthetic resin tobe filled in the cavity during the dwelling and filling process isrepresented by the following formula with a weight value G:

    G=(1V.sub.I -1/V.sub.H)×V+A×X/V.sub.H

wherein: V_(I) is a specific volume value of plasticized synthetic resinplaced at its forward movement side of the front end of the screw in thecylinder immediately before the injection operation; V_(H) is a specificvolume value of the plasticized synthetic resin placed at its forwardmovement side of the front end of the screw in the cylinder during thedwelling process; V is a volume of the plastifiable synthetic resinplaced at its forward movement side of the front end of the screw in thecylinder immediately before the injection operation; A is an internalsectional area of the cylinder; and, X is a travel distance of the screwfrom immediately before the injection to the dwelling operation.
 6. Themolding cycle control method of an injection molder as set forth inclaim 1, wherein the suck-back process is carried out with theplasticized synthetic resin placed in the gate of the mold solidifiedand blocked from flowing in the gate.
 7. The molding cycle controlmethod of an injection molder as set forth in claim 1, wherein thesuck-back process is conducted during the measuring process.
 8. Themolding cycle control method of an injection molder as set forth inclaim 1, wherein after the completion of the measuring process, the flowpassage opening and closing mechanism is open and the suck-back processis carried out.
 9. A control method for an injection molder comprising acylinder having a screw therein and a flow passage opening and closingmechanism between the cylinder and a gate of a mold having mold cavityto selectively block the flow of resin between the cylinder and themold, the method comprising:a filling step comprising advancing thescrew in the cylinder with the flow passage opening and closingmechanism open to inject resin from the cylinder into the mold cavity; adwelling step comprising applying a predetermined pressure to the resininjected into the cavity of the mold with the screw; a measuring stepcomprising closing the flow passage opening and closing mechanism whilethe predetermined pressure is being applied, and retracting the screw tomeasure a predetermined amount of resin in the cylinder for the nextmolding cycle while the flow passage opening and closing mechanismremains closed; a suckback step occurring after the resin has solidifiedin the gate of the mold comprising opening the flow passage opening andclosing mechanism and retracting the screw to reduce the pressure on theresin between the front of the screw and the gate.
 10. The methodaccording to claim 9 wherein the measuring step comprises a firstmeasuring step in which the a first predetermined amount of resin ismeasured in the cylinder before the suckback step, and a secondmeasuring step in which an additional amount of resin is measured in thecylinder after the suckback step and prior to the next molding cycle.